Key Elements of the Clean Air Act

How Smog is Formed

Many pollution sources,
including cars, manufacturing
and chemical plants, and
products used in homes,
release smog-forming
pollutants. Winds blow the
pollutants away from their
sources and the heat of the
summer sun causes chemical
reactions that form groundlevel
ozone-a principal
component of smog.

Hours after the smog-forming
pollutants are released from
their sources, smog pollutes
the air, often many miles away
from where the pollutants
were released.

EPA's mission is to protect human health
and the environment. To achieve this
mission, EPA implements a variety of
programs under the Clean Air Act that
focus on:

reducing outdoor, or ambient, concentrations of air
pollutants that cause smog, haze, acid rain, and other
problems;

reducing emissions of toxic air pollutants that are
known to, or are suspected of, causing cancer or
other serious health effects; and

phasing out production and use of chemicals that
destroy stratospheric ozone.